5V

1.8V

Master Power

Supply

SS/TRACK

LM2745/8

1 k:

150:

10 k:

5 k:

FB

LM2745, LM2748

www.ti.com

SNOSAL2E – APRIL 2005 – REVISED APRIL 2013

Figure 19. Tracking Circuit

One way to use the tracking feature is to design the tracking resistor divider so that the master supply’s output

explicitly showing the power components) both rise together and reach their target values at the same time. For

should be set higher than the feedback voltage of 0.6V (say about 0.65V as in the above equation). If the master

give the two supplies identical soft-start times would be 150

Ω. A timing diagram for the equal soft-start time case

is shown in Figure 20.

Figure 20. Tracking with Equal Soft-Start Time

TRACKING A VOLTAGE SLEW RATE

The tracking feature can alternatively be used not to make both rails reach regulation at the same time but rather

to have similar rise rates (in terms of output dV/dt). This method ensures that the output voltage of the LM2745/8

always reaches regulation before the output voltage of the master supply. In this case, the tracking resistors can

be determined based on the following equation:

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